Dr. Alex Krasnok

Nonlinear dielectric nanophotonics

Most experts believe that the creation of all-optical transistors is the key to creating the next generation of computers: optical computers. This is because current computing power is limited by the time needed to trigger modern transistors, which is between 0.1 and 1 nanoseconds due to the use of electrons to carry the signal in these systems. However, optical computers use photons to carry useful signal, and this means that the amount of information passing through the transistor per second is increased by something on the order of 1,000-fold. In this research, I have forwarded a new approach for designing such optical transistors and even made a prototype from a single silicon nanoparticle. Through various experiments and theoretical efforts, I have discovered that the properties of the silicon (Si) nanoparticle can be drastically changed through irradiating it with ultrashort laser pulses, which cause ultrafast photoexcitation of electron-hole plasma, the presence of which alters the dielectric permittivity of the Si nanoparticle for a matter of picoseconds. I have found that this change allows for the control of the direction in which light is scattered. This capability is exactly what is necessary for the creation of all-optical transistors. In particular, in Refs. [1] a conceptually new modulation principle based on power pattern reconfiguration via electron-hole plasma photoexcitation is proposed. The operation speed of the proposed modulator is about few ps and the modulation depth is 20% that is enough for practical applications. The realized operation speed complies with modulation of an optical signal at the level of 100-1000 GHz, that is by several orders of magnitude greater than the electrical counterparts.

My consequent studies paved the way to use dielectric nanostructures for high-harmonic generation [2], boosting the luminescence from quantum emitters, scattering engineering, ultrafast switchers and modulators [2], optical interconnections on a chip, and enhanced Raman scattering. Interesting photonic phenomena such as Fano resonances, Purcell effect, and strong coupling in dielectric nanostructures have been also demonstrated in my works.